1. Field of the Invention
The present invention relates generally to pressure relief systems and, more particularly, to a rupture disc assembly for use in relieving excess pressure in low-pressure processing applications where it is desirable that sanitary conditions be maintained. It is especially useful in dairy, brewery, food processing and similar sanitary applications where frequent disassembly, cleaning and reassembly of the rupture disc assembly is required.
2. Description of the Prior Art
As explained in U.S. Pat. No. 5,267,666, entitled Multiple-Dome, Scored, Rupture Disc, owned by the assignee hereof (herein the '666 patent), and which is incorporated herein by specific reference thereto, rupture disc assemblies have long been used to relieve pressure in industrial applications for venting excess pressure within pressurized components or equipment in order to prevent damage to the equipment.
In the '666 patent, it is pointed out that conventional forward-acting rupture discs include a unitary disc having a circular central dome region and an outer annular flange. The dome presents a concavo-convex shape corresponding to the size of the relief passage within which the disc is positioned, and the disc is oriented with the concave surface of the dome in contact with the pressure to be relieved. A line of weakness is provided in the disc which substantially circumscribes the dome except for a small hinge portion of the circumference of the central dome region.
Conventional forward-acting discs typically are operated only at pressures up to 80% of that at which the disc is designed to burst in order to preclude premature rupturing. For this reason, reverse-acting rupture disc assemblies having knife blade components are frequently used because they can handle normal operating pressures up to about 90% of the rated pressure of the disc.
The invention of the '666 patent represented an important step forward in the art by elimination of the need for complex knife structure, including the size, location within the assembly, and operation of the knife. This desired result was accomplished through the provision of a pair of semi-circular, side-by-side bulges within the central region of the disc, which were separated by a diametrically extending ridge. Knife blade rupture disc assemblies do not lend themselves though to applications where frequent disassembly of the unit is required in order to maintain required sanitary conditions.
In the knife-less multiple dome rupture disc of the '666 patent, the diametrical ridge dividing the central region of the disc into two separate bulges, functioned as a beam to cause the bulged region of the disc to first separate from the planar annular disc section, before separating from the remainder of the planar disc section. The result was positive operation of the disc at a relatively low differential pressure at levels equal to at least about 90% of the burst rating of the disc.
The reverse-acting rupture discs which employed knives, however, did not lend themselves to use in sanitary applications such as dairy product processing operations because of the difficulty in disassembling the knife blade rupture disc assemblies, and to carry out a cleansing operation, particularly on a very frequent basis as required in sanitary equipment requirements.
Even though the multiple-dome, scored, rupture disc of the '666 patent did offer potential advantages in sanitary applications as a replacement or substitute for knife-operated disc assemblies, it was found to be difficult to manufacture multiple-dome discs which offered positive rupture characteristics at relatively low pressures, i.e., 30 psig or even lower in the case of a disc having a rupture area diameter of the order of 11/4 to 11/2 inches. Lower than expected burst pressures can also be obtained with larger diameter discs.